1. Field of the Invention
This invention is related generally to liquid crystal devices for controlling properties of light, and, more particularly, to use of fast response of liquid crystal molecules near boundary surfaces in combination with long interaction lengths of planar waveguide structures for fast control of polarization.
2. State of the Prior Art
It is often necessary for light beams, such as those used to transmit data, generate control signals, and many other applications to be polarized in a particular manner or in a particular state of polarization in a waveguide for purposes of routing, multiplexing, demultiplexing, signal processing, and other purposes. However, such desired polarization as well as phase relationships and other properties can become attenuated or degraded as the light propagates through various media or devices, or the polarization and/or phase may have to be changed or adjusted to correlate or combine with another beam of a different polarization state. Even after a particular desired polarization state is set, temperature changes, mechanical pressure or tension on optical fibers or other optic components, and many other variables can cause the polarization state of light to undergo changes.
Polarization controllers are used to set, recondition, or readjust polarization of light beams for these and other purposes. Practical considerations require that polarization controllers for such purposes be electrically controllable, and it is desirable that they respond fast to electric control signals. Liquid crystal materials have the largest electro-optic response of all currently known materials, and they are relatively easy to incorporate into optical devices. Therefore, they are used in many polarization controllers as well as in controllers of other light properties. However, the primary drawback of such ordinary liquid crystal polarization control devices is that their response times to changing electric fields, typically measured in tens of milliseconds, is slower than that required for many polarization controller applications.
Another class of crystalline materials, lithium niobate (LiNbO3), is much faster, with response times that can modulate light in gigahertz frequencies, and they can be used in applications that require faster response times than ordinary liquid crystals. However, LiNbO3 is also very expensive to incorporate into devices, because it does not lend itself to high-volume manufacturing processes and requires tedious polishing. Further, while the tens of milliseconds speed of ordinary liquid crystal devices is too slow for many applications, the super-fast, gigahertz modulating frequency capabilities of LiNbO3 are impressive, but unnecessary and do not justify the expense for many applications. Therefore, there is a need for light control devices, such as polarization controllers, that respond to electric control signals significantly faster than ordinary liquid crystal devices, but which are less expensive and easier to manufacture than the super-fast LiNbO3 devices.
Additional objects, advantages, and novel features of the invention are set forth in part in the description that follows and others will become apparent to those skilled in the art upon examination of the following description and figures or may be learned by practicing the invention.